diff options
Diffstat (limited to 'third_party/heimdal/lib/hcrypto/libtommath/bn_mp_reduce_2k_l.c')
-rw-r--r-- | third_party/heimdal/lib/hcrypto/libtommath/bn_mp_reduce_2k_l.c | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_reduce_2k_l.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_reduce_2k_l.c new file mode 100644 index 0000000..6a9f3d3 --- /dev/null +++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_reduce_2k_l.c @@ -0,0 +1,49 @@ +#include "tommath_private.h" +#ifdef BN_MP_REDUCE_2K_L_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ + +/* reduces a modulo n where n is of the form 2**p - d + This differs from reduce_2k since "d" can be larger + than a single digit. +*/ +mp_err mp_reduce_2k_l(mp_int *a, const mp_int *n, const mp_int *d) +{ + mp_int q; + mp_err err; + int p; + + if ((err = mp_init(&q)) != MP_OKAY) { + return err; + } + + p = mp_count_bits(n); +top: + /* q = a/2**p, a = a mod 2**p */ + if ((err = mp_div_2d(a, p, &q, a)) != MP_OKAY) { + goto LBL_ERR; + } + + /* q = q * d */ + if ((err = mp_mul(&q, d, &q)) != MP_OKAY) { + goto LBL_ERR; + } + + /* a = a + q */ + if ((err = s_mp_add(a, &q, a)) != MP_OKAY) { + goto LBL_ERR; + } + + if (mp_cmp_mag(a, n) != MP_LT) { + if ((err = s_mp_sub(a, n, a)) != MP_OKAY) { + goto LBL_ERR; + } + goto top; + } + +LBL_ERR: + mp_clear(&q); + return err; +} + +#endif |